Influence of Crimped Steel Fibre on Properties of Concrete ...

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Abstract

This research was inspired by the growing global shortage of natural aggregates. Different types of waste ceramics (apart from recycled concrete) are the most popular materials for the production of waste aggregates as possible substitutes for natural ones. The aim of this research was to analyse the efficiency of different aggregate mixes composed of waste and natural materials focusing on two waste ceramic aggregates, which were prepared concrete mixes based on specifically composed aggregates (blend of natural aggregate, porous and iron oxide-rich (red) waste ceramic aggregate, and dense, kaolin-based (white) waste ceramic aggregate). All aggregates were thoroughly tested before utilisation for concrete mix creation. Altogether, four blends of aggregates were prepared in order to prepare concrete mixes using a simplex experiment design. The mixes were then modified by adding various amounts of crimped steel fibre. Such properties of hardened steel fibre-reinforced concrete (SFRC) such as density, compressive strength, shear strength, ultrasound propagation velocity, dynamic modulus of elasticity, and limit of proportionality during flexural testing were of special interest. Tests were conducted according to European and Japanese standards. The achieved fibre-reinforced concretes were characterised by satisfactory strength characteristics, thereby enabling the substitution of traditional reinforcement. Strength classes according to the fib Model Code were assigned.

Keywords:

aggregate, white ceramic, red ceramic, waste, fibre, SFRC

1. Introduction

A growing research effort exists globally to successfully harness different ceramic wastes in the construction industry [1,2,3], resulting in some successful applications of different types of waste ceramics as partial full substitutes of fine and coarse natural aggregates [4,5,6]. The type of waste ceramic most often considered for harnessing as a waste aggregate is red (porous, iron oxide-rich) ceramic [4,7], with multiple types of nonstructural concrete elements characterised by less demanding strength characteristics being cast using this kind of waste aggregate [8]. In order to utilise waste ceramic aggregates for the production of structural concrete, a new approach to composition is needed. Different waste ceramic aggregates could be blended together (e.g., red waste ceramic aggregate and white (dense, kaolin-based) waste ceramic aggregate) to achieve a new level of quality in sustainable concrete production, thereby enabling the shaping of aggregate properties to utilise their advantages and harness synergy. Red ceramic is characterised by limited compressive strength due to its porosity (usually between 10 and 15 MPa), but has the advantage of using an internal curing process [7]. White ceramic is characterised by &#;no porosity&#; and a much higher compressive strength red ceramic. This research was conducted to prove the proposed novel concept of using waste ceramic aggregates, in which red ceramic obtained from brick production waste and white ceramic obtained from local pottery factory production waste were used as waste aggregates. Both ceramics were processed using the same machinery and grinding procedure to achieve waste aggregates. As a reference, the properties of natural post-glacial aggregates commonly available in countries located along the southern shoreline of the Baltic Sea [9] were chosen. Utilisation of a mixture design was enabled using three aggregates, where the sum of the volume of all three ingredients was always equal to 100%. The mixture design allowed the visualisation of results in the form of ternary contour plots, which are commonly used in technology of binders [10] and concrete [11].

The research programme was divided into two stages. The first stage covered the testing of the geometrical and mechanical properties of the waste and natural aggregates. The second stage covered property testing of concretes made on the basis of the waste and natural aggregates that were tested during the first stage. Analysis of the possible replacement of natural aggregates by waste ceramic aggregates was subsequently conducted. Specific mixtures of both waste ceramic and natural aggregates were proposed for concrete production. The obtained four mixes were subsequently modified by the addition of steel fibres, which were added in volumes ranging from 0.5% to 1.5% (Vf). Altogether, 16 mixes of concrete were cast in order to test the properties of the concretes in a hardened state.

3. Experimental Design

An ordinary integral simplex design (also known as a mixture design) [21] was utilised in this research. The three types of aggregate were named as follows: X&#;red ceramic waste; Y&#;natural aggregate; Z&#;white ceramic waste. Due to the different specific gravity values of red ceramic waste, white ceramic waste, and natural aggregate, the materials were dosed by volume. The specific property of the mixture design was that the sum of the volume of all three ingredients was always equal to 100%. In this case, the three aggregates played the roles of the ingredients. The utilised design is described in detail in .

Table 3

Mix No.Aggregate (%)Natural AggregateWhite Ceramic WasteRed Ceramic WasteIIIIIIIVOpen in a separate window

The object of the experiment was considered to be a complex composite material. The internal structure of the material was unavailable (for unknown reasons) to observers, with only the &#;input&#; and &#;output&#; parameters known to observers [22,23]. All achieved experimental results were statistically processed. The Smirnov&#;Grubbs criterion was used to assess gross error of the values. The sequence of specific test realisations was decided using a digital random number generator to guarantee objectivity. All calculations associated with the execution of the research and graphic interpretation of the mathematical model were carried out using the Statistica 12 software suite. Contour plots were created using a polynomial fit with fitted functions characterised by a correlation coefficient of at least 0.80. This type of experimental design was successfully used numerous times in concrete technology, including concretes based on waste aggregates and steel fibre-reinforced concretes [21]. The number, shape, and size of specimens utilised for each test are presented in .

Table 4

Type of TestSpecimen Shape (cm)Number of SpecimensStandardIn One TestTotalDensityCube 15 × 15 × 15
Beam 70 × 15 × 153
396EN -7: *Compression strengthCube 15 × 15 × EN -3: *Shear strengthBeam 70 × 15 × JCI-SF6: **Ultrasound propagation velocityBeam 70 × 15 × EN -4: *Dynamic modulus of elasticity ***Beam 70 × 15 × EN -4: *Flexural strength: LOP
(limit of proportionality)Beam 70 × 15 × EN : *Open in a separate window

All specimens were tested after 28 days of curing (first day in a plastic mould covered by a polyethylene sheet, then 27 days in a water tank) in a temperature of 20 °C ± 0.5 °C. After curing, specimens were measured, weighed, and dried to avoid problems during the ultrasound velocity test [25]. The calculated density was a general quality test of the prepared specimens, with the value of density also useful for the ultrasound propagation velocity test and for computing the dynamic modulus of elasticity value. The shear strength test was performed on half of the beams that remained after the flexural test. Concrete mixes were modified by adding steel fibres to proportions of 0.5%, 1%, and 1.5%. The achieved results were subsequently compared with results obtained by other researchers working on steel fibre-reinforced concrete. Altogether, 16 concrete mixes were cast in order to test the properties of steel fibre-reinforced concrete (SFRC) in the hardened state.

5. Discussion

Four residual strengths (fR1, fR2, fR3, fR4) associated with particular CMOD values (0.5, 1.5, 2.5, and 3.5 mm) are not feasible for the direct design of an SFRC mix. There is general agreement among the global SFRC research community that the first residual strength fR1 is important in terms of service conditions, whereas the third residual strength fR3 is recognised as a key factor for the assessment of ultimate conditions. The &#;fib Bulletin 55, Model Code &#; proposed the utilisation of the first and third residual strengths to calculate both the serviceability limit state (SLS) and the ultimate limit state (USL). Basically, the ratio fR3/fR1 was defined to describe the relationship between the behaviour of SFRC at ULS and SLS [32,33].

The proposed fib strength classification of SFRC consisted of two elements, i.e., strength interval (namely fR1) and post-cracking softening or hardening behaviour, which was described by a letter symbol from a to d directly referring to the fR3/fR1 ratio. Letter a represents the strongest softening and letter d represents the strongest hardening [34].

When the fibre reinforcement was efficient enough, substitution of traditional bar and stirrup reinforcement was enabled. Two following conditions were fulfilled simultaneously to pass the substitution threshold:

fR1 / fLOP > 0.4

(2)

fR3 / fR1 > 0.5

(3)

Calculated values of the above factors for tested concretes are presented in with the associated strength class and reinforcement substitution.

Table 5

Concrete Symbol fR3/fR1 fR1/fLOP fLOP (MPa)Strength ClassReinforcement SubstitutionI0....0bEnabledII0....0aEnabledIII0....0bEnabledIV0....0bEnabledOpen in a separate window

The achieved strength classes and enabled traditional reinforcement substitutions allowed for the utilisation of the tested concretes for structural applications. The wise use of different blends of ceramic waste and natural aggregates to shape the properties of cast concretes is possible. The proposed approach toward ceramic waste aggregates merged the advantages of internal curing and fibre reinforcement and was proven to be efficient.

6. Conclusions

The following conclusions can be drawn from the research described in this paper:

• It is possible to cast composites based on multiple waste aggregates;

• A blend of waste ceramic aggregates achieved a greater flexural strength of a cement composite than ordinary natural sand;

• The highest compressive strength was achieved using only natural aggregates;

• The compressive strength of the tested concretes was significantly influenced by the composition of the aggregate mix, as evidenced by the concrete with 1.5% fibre composition, whereby the values ranged from 17.5 MPa to 85.3 MPa;

• It is possible to partially or fully substitute natural aggregates with white or red ceramic wastes;

• The composites created on the basis of the white and red ceramic wastes are characterised by satisfactory mechanical properties, allowing for the assignment of standard strength classes according to both the EN and fib Model Code ;

• The research programme should be continued using greater specimens, focusing on more complicated mechanical characteristics (e.g., dynamic properties) of composites to enable full-scale modelling.

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Acknowledgments

The authors would like to thank Katarzyna Maciejewska and Elzbieta Kuźmińska for their help in the preparation of the specimens and during some of the conducted testing procedures.

Author Contributions

Conceptualization, J.K. (Jacek Katzer); Data curation, J.K. (Jacek Katzer) and J.K. (Janusz Kobaka); Formal analysis, T.P.; Funding acquisition, T.P.; Investigation, J.K. (Janusz Kobaka); Project administration, T.P.; Software, J.K. (Janusz Kobaka); Writing &#; original draft, J.K. (Jacek Katzer); Writing &#; review & editing, J.K. (Janusz Kobaka). All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding

Conflicts of Interest

The authors declare no conflict of interest

Unleashing the Strength: Exploring the Advantages of Steel Fiber Reinforced Concrete
Understanding Steel Fiber Reinforced Concrete and the benefits of incorporating steel fibers in concrete

Steel fiber reinforced concrete (SFRC) is a composite material that combines traditional concrete with steel fibers. Adding steel fibers enhances the concrete's properties, making it more robust, durable, and resistant to cracking. SFRC is widely used in various construction applications, including buildings, highways, bridges, and pavements.

Introduction

Concrete is a material known for its hardness and durability. However, it is also brittle and can easily crack or chip when subjected to tensile or flexural forces. Earlier, liquid concrete was poured over steel bars during construction to create a more robust and durable structure. Steel bars used in construction can expand and contract with temperature changes; hence, placing the concrete on slabs with expansion joints between them was recommended. But times change!

Then came a time when a concrete floor without expansion joints was desired!
At a very early age in the steel fiber industry, TOCO Steels Pvt. Ltd. developed various highly technologically advanced and durable products called Steel fibers, which were reinforced into concrete to achieve higher strength than steel bars.

With its remarkable strength and improved crack resistance, Steel Fiber Reinforced Concrete offers numerous benefits for structural elements subjected to heavy loads and harsh environmental conditions. From industrial flooring to tunnel linings, steel fiber-reinforced concrete demonstrates exceptional toughness and durability.
As the demand for durable and high-performance construction materials continues to rise, the application of Steel Fiber Reinforced Concrete (SFRC) has gained significant attention. 
In this article, we will delve into the advantages of SFRC, highlighting its potential to revolutionize the construction industry.

What are the advantages of steel fiber-reinforced concrete?

• Increased Strength and Load-Bearing Capacity  

One of the primary advantages of Steel fiber concrete is its increased strength and load-bearing capacity. The steel fibers in the concrete act as reinforcement, improving its tensile strength and allowing it to withstand heavy loads. This makes SFRC an ideal choice for structures that require high strength and durability, such as skyscrapers, bridges, and dams.

• Improved Crack Resistance

Cracking is typical in concrete structures, especially under stress or extreme weather conditions.
However, SFRC offers improved crack resistance compared to traditional concrete. The steel fibers distribute stress evenly throughout the concrete. This helps maintain the structural integrity of the concrete and increases its lifespan.

• Enhanced Durability and Longevity

SFRC exhibits enhanced durability and longevity compared to traditional concrete. 
The steel fibers provide additional reinforcement, making the concrete more resistant to wear, impact, and environmental factors. This results in a longer service life for SFRC structures, reducing the need for frequent repairs or replacements, and ultimately saving costs over time.

• Increased Flexural Properties

Flexural strength is crucial in structures that need to withstand bending forces, such as beams and slabs. The benefits of using SFRC offer improved flexural properties thanks to the steel fibers' ability to distribute forces more efficiently.

• Reduced Maintenance Costs

The need for frequent repairs and maintenance due to cracks or structural issues is significantly minimized by using steel fiber-reinforced concrete. This saves money and reduces the disruption caused by maintenance activities.

• Versatility in Design and Construction

The benefits of incorporating steel fibers in concrete provides greater versatility for design and construction of concrete structures. Adding steel fibers allows for more flexible design options, such as thinner and lighter structures. This opens possibilities for innovative and creative architectural designs while maintaining strength and durability.

• Faster Construction Time

Another advantage of SFRC is its potential for faster construction times.
Using steel fibers eliminates the need for traditional reinforcement methods, such as installing steel bars or meshes. This simplifies the construction process and reduces labour and installation time, saving overall project time.

The uses of steel-fiber-reinforced concrete

The steel fibers manufactured by TOCO Steels Pvt. Ltd finds application in various construction projects. Here are some common uses:

• Highway and Bridge Construction: SFRC is widely used to construct roads and bridges. The enhanced strength and durability of SFRC make it suitable for withstanding heavy traffic loads and harsh weather conditions.
• Building Construction: SFRC is increasingly used, particularly in high-rise structures. Its improved strength, crack resistance, and durability make it an ideal choice for tall buildings.
• Pavements and Industrial Floors: SFRC is commonly used in pavements and industrial floors due to its ability to withstand heavy traffic and resist wear. The steel fibers enhance the concrete's abrasion resistance, making it suitable for high-traffic areas
• Precast Concrete Elements: SFRC is also used to produce wall panels and structural components. Adding steel fibers enhances these elements' strength and performance, ensuring their structural integrity.
• Tunnels and Underground Structures: SFRC applies to constructing tunnels and underground structures. The enhanced durability and crack resistance of SFRC make it suitable for withstanding the challenging conditions found in underground environments.

UHPC structures

TOCO Steels also manufactures micro steel fibers for Ultra high performance concrete (UHPC), believing in preserving your infrastructure. Below are some of the applications where UHPC, made with micro steel fibers is used:

• Architectural structures: UHPC finds applications in architectural features like facades, countertops, and decorative elements due to its ability to achieve intricate shapes and textures while maintaining strength.
• Wind turbine towers: UHPC components enable the construction of taller wind turbine towers, leading to increased energy output and more renewable energy generation.
• Dams and locks: Dams and locks are constantly exposed to water and ships, which can cause significant abrasion, leading to corrosion and loss of structural strength. To combat this, construction and retrofitting with field cast or shotcrete Ultra-High Performance Concrete (UHPC) can provide a highly durable solution against abrasion and a high-strength barrier against ship impacts.
• Bridge girders: Bridge girders play a crucial role in supporting bridge decks and traffic loads, especially for short- and medium-span bridges. To ensure maximum strength and durability, Ultra-High Performance Concrete (UHPC) is the ideal choice. Its exceptional properties make it a reliable and cost-effective solution for bridge construction.
• Bridges: Its remarkable compressive strength allows for longer spans, reducing the need for intermediate supports and creating sleek, aesthetically pleasing designs. Additionally, UHPC's resistance to corrosion makes it ideal for bridge decks that are exposed to harsh weather conditions or de-icing salts.
• Seismic columns: UHPC is ideal for seismic columns in bridges, thanks to its strength and durability. This technology can be used to design innovative and earthquake-resistant bridge columns
• Tunnels and parking structures: Its resistance to cracking and high load-bearing capacity ensure long-term performance even under heavy traffic or extreme conditions.
• Precast concrete elements: With its superior mechanical properties, UHPC enables the creation of thin, lightweight panels that can be used for cladding buildings or as structural components. This not only enhances design possibilities but also reduces material usage and transportation costs.
• Security safe: For security vaults for financial institutions, UHPC (made with a mixture of micro-steel fibers) is the ideal choice. When it comes to ensuring the safety and security of the panels or vault doors, compressive strength is the only factor that is prioritized. With the advancement of technology, UHPC helps create a concrete panel that is thinner and lighter in weight than standard concrete.

The Future of Steel Fiber Reinforced Concrete

SFRC has a promising future in sustainable building practices. Incorporating recycled steel fibers reduces its environmental impact. SFRC's ability to create thinner and lighter structures promotes sustainability. With advancing technology and research, SFRC's properties and performance are expected to improve, opening up new possibilities for construction projects.

Conclusion

At TOCO Steels Pvt. Ltd, we have become a pioneer in manufacturing high-quality steel fibers in various shapes that are revolutionizing the construction industry worldwide.
Utilizing SFRC, builders and engineers can construct robust, long-lasting, and environmentally friendly structures.
Build with confidence. 

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